In manufacturing semiconductor devices, a variety of heat treatment apparatuses are being used to perform treatments, e.g., oxidation, diffusion, and CVD (Chemical Vapor Deposition), on target semiconductor wafers. In general, a heat treatment apparatus includes a processing vessel configured to accommodate therein a semiconductor wafer, a cylindrical heat insulating member covering the periphery of the processing vessel, and a heat treatment furnace having a heater provided at the inner circumferential surface of the heat insulating member to heat the semiconductor wafer accommodated in the processing vessel.
For a heater for use in a batch type heat treatment apparatus, for example, there are used heater elements which are supported by supports disposed along the inner wall of a cylindrical heat insulating member and heat the inside of a furnace to be in a range from about 800 degree C. to about 1000 degree C. Further, the heat insulating member is made by baking insulation material, for example, made of ceramic fiber, into a cylindrical shape, and thus heat loss due to radiation or conduction of heat can be reduced and efficient heating can be made. Furthermore, the supports are made of, for example, ceramic, and support the heater elements with a predetermined pitch so as to allow thermal expansion or contraction of the heater elements.
Meanwhile, the heater elements are provided at the inner circumferential surface of the cylindrical heat insulating member in such a manner that one heater element is provided at each half circumferential surface when the inner circumferential surface of the heat insulating member is vertically divided into two half circumferential surfaces. In this case, a first and a second heater element respectively provided at a first and a second half circumferential surface operate independently.
Further, each of the heater elements has a plurality of columnar portions, each columnar portion extending in a circumferential direction and provided in multi-stages, and a connecting member extending in a vertical direction and connecting the columnar portions.
However, it is difficult to provide conventional heater elements having the above-described configuration at the entire inner circumferential surface of the heat insulating member, and it is also difficult to heat semiconductor wafers uniformly with such conventional heater elements.